Boom lift control system



United States Patent 3,334,756 BOOM LIFT CONTROL SYSTEM William A. Whitmire, Castro Valley, Califi, assignor to Bigge Drayage Co., San Leandro, Calif., a corporation of California Filed Sept. 9, 1966, Ser. No. 578,226 6 Claims. (Cl. 21239) This invention relates to construction cranes with movable booms, and more particularly to a system for controlling the raising and lowering of a crane boom within predetermined limits.

Construction cranes often must be operated at locations within close proximity to obstructions such as buildings and electrical wires. Under such circumstances absolute control of the crane boom movement is essential in order to avoid serious accidents which could involve both injuries and property damage. Experience in the field long ago established the fact that operators skill cannot be relied upon to control the boom movements within safe limits under all conditions.

A general object of the present invention is to pl'Ovide a safety control system for automatically stopping either the upward and downward movement of a crane boom when it reaches either an upper or lower limit which has been preset to define a predetermined range of travel during its normal operation.

Another object of the invention is to provide a system for controlling the upward and downward travel of boom cranes within predetermined limits that is easily adaptable for operation in conjunction with either pneumatically, hydraulically or electrically controlled boom drive systems on existing cranes without altering their normal operation.

Other important objects of my invention are to provide a system for controlling boom up and down travel within predetermined limits that is easy to adjust to the exact desired limits of boom travel without the need for skilled labor or special tools; that is easy to install and to service; and that is particularly well adapted for ease and economy of manufacture.

Construction cranes of the type adapted for handling heavy loads generally utilize a power drive mechanism which acts through gears 'and a clutch to elevate and lower the boom. The clutch is usually operated hydraulically by means of manual controls available to the operator in the crane cab. The present invention contemplates an arrangement wherein the clutch for the boom elevating drive is controlled automatically to stop the boom when it reaches a predetermined up or down position. In the crane cab the actual up or down travel of the boom causes a linear movement of a cable to which are attached a pair of actuators. Adjacent to the linearly traveling cable are a pair of limit switches that can be adjusted to various spaced apart locations. The location of each limit switch establishes the position of the boom, that is, when each switch is engaged by an actuator, the clutch operates to disengage the boom drive mechanism.

Other objects, advantages and features of the invention will become apparent from the following detailed description thereof taken with the drawings, in which:

FIG. 1 is a partially diagrammatic view showing a boom limit control system embodying the principles of the present invention;

FIG. 2 is an enlarged view in section 22 of FIG. 1;

FIG. 3 is a fragmentary diagrammatic view showing the present invention in combination with a pneumatic clutch control system;

FIG. 4 is a fragmentary diagrammatic view showing the present invention in combination with an electrical clutch control system.

taken along line 3,334,756 Patented Aug. 8, 1967 Referring to the drawings, FIG. 1 shows schematically a boom control system 10 embodying the principles of the present invention which is operably connected to control the up and down movement of a boom. To conserve space, only the lower half of a boom 12 is shown, where it is pivotally connected at one end forming a hub portion 14 to a crane chassis 16.

The normal raising and lowering of the boom, which occurs as it is caused to pivot about its hub portion, is controlled by a suitable drive system generally including a prime mover which is controllably connectable by clutch means to a drum that controls cables connected to the boom. The aforesaid arrangement can have many forms and since it is not in itself critical to the invention, the prime mover drum and clutches and cable rigging are not shown in the drawings. The automatic control features of the present invention are accomplished by control of both the boom up and boom down clutch members as will be seen from the following description. Attached to and extending at least partially around the hub portion 14 of the boom is a flexible cable 18, the end of which is fixed to the hub portion by a suitable means. Since the hub portion is essentially cylindrical, the raising or lowering of the boom at a constant rate, and thus the rotation of its hub portion, causes movement of the cable at a linear rate proportional to the boom angular rate. From the boom the cable 18 extends into the cab of the crane, which is not shown in the drawing. Within the cab the cable passes over a first pulley 20 which is preferably mounted with an elongated housing 22 that may be fixed to a suitable structural member within the crane Cab. This first pulley is mounted at one end of the housing and is aligned with a second pulley 24 at the other end of the housing around which the cable extends. The end of the cable is attached to a spring 26, or some suitable tension producing and take-up means, which in turn is anchored to the end of the housing near the first pulley.

Adjustably attached to the cable 18 are a pair of switch actuators 28 and 30 which are adapted to control the upper limit and the lower limit of boom travel. As seen also in FIG. 2, each actuator comprises a lower tab portion 32 for engaging a limit switch and an upper integral cable gripping portion 34. The latter includes a pair of jawlike members and an upwardly extending shank portion 36 which retains a set screw 38. With the cable between the members 34 the set screw can be tightened to hold the actuator firmly to it at a preset position. The upper side of the housing 22 is provided with a slot 40 through which the upper portions 34 of the actuators extend, the slot 40 serving to keep the actuators 28 and 30 aligned as they are moved back and forth by the cable. Fixed inwardly from the pulleys 20 and 24 near opposite ends of the boom control housing 22 are a pair of limit switches 42 and 44 which are so aligned that they may be tripped when engaged by the actuators 28 and 30, respectively. In the embodiment shown in FIG. 1, these switches are connected in parallel to a battery 44 through a pair of electrically operated hydraulic safety valves 46 and 48.

The boom movement in conventional cranes as shown schematically is generally controlled by an operators lever 50 which may be pivoted about a support 52 fixed to the crane structure. Attached to the lever on opposite sides of the pivotal support are a pair of links 54 and 56 which operate a pair of control valves 58 and 60. Each of the control valves is supplied with hydraulic fluid from a supply tank 78 or from some pressure source through a conduit 61 to inlets 62 and 64, respectively. The valve 58 has an outlet conduit 66 connected to a clutch actuator 68 for causing the boom to move up, and similarly, the valve 60 has an outlet conduit 70 connected to a clutch actuator 72 for causing a boom down movement.

As shown in the drawing, the actuators 68 and 72 may be hydraulic slaves of the valves 58 and 60. Thus, under normal operation, a movement of the operators lever in one direction causes one control valve to open and the other control valve to close, and hydraulic pressure is supplied from the open control valve to its clutch actuator. This engages the power drive mechanism (not shown) to raise or lower the boom, as the case may be.

A T-connected conduit 74 extends from the conduit 66 to the inlet side of the hydraulic safety valve 46 and similarly, a T-connected conduit 76 extends from the conduit 70 to the inlet side of the hydraulic valve 48.

When the boom is being normally operated within its preset safe vertical limits, the safety valves 46 and 48 are both closed. However, when either of the hydraulic valves is opened, it allows hydraulic fluid to flow through it directly to the storage tank 78. This in turn relieves the pressure in the conduit to the particular clutch actuator and disengages the clutch to stop the boom. The safety valve 46 or 48 must close again before the boom can operate normally, and it will close if the operators lever 50 is moved in the opposite direction to put the other clutch into engagement, causing the boom to move in the opposite direction.

On various production cranes, pneumatic or electrical clutch actuation devices are utilized instead of the hydraulic system shown in FIG. 1. However, such clutch actuation devices may be automatically controlled by the limit switches 42 and 44 of the present automatic system in substantially the same manner as described above. For example, FIG. 3 shows schematically a valve 80 of the type which may be utilized in a pneumatic clutch actuation system. It may be a standard three-way valve which is actuated by a solenoid 82. When the boom reaches a preset limit and the valve 80 is actuated, air in a conduit 84 from a pressure source or from the operator controlled valve that normally acts to maintain the clutch in engagement through a passage 85 in the valve 80 and an outlet conduit 86 is shut ofi. As shown, the air that was activating the clutch is exhausted from the actuating piston through a valve passage 87 and an exhaust 88, thereby causing the clutch to disengage.

FIG. 4 shows an arrangement where the boom drive clutch is normally engaged electrically. Here, a safety control valve 90 serves as a circuit breaker 92 to disrupt the electrical continuity through a lead 94 from the operators control and through a contact 96 and an output lead 98 to an electrically actuated clutch, thereby causing the latter to disengage automatically. The foregoing is merely illustrative of the versatility of my control system and its adaptability to the various boom drive and operating control systems.

The operation of my automatic boom control system should be readily apparent from the foregoing but will be reviewed briefly. With the boom 12 first elevated to the desired angle defining the upward travel limit, the upper limit actuator 30 is moved on the cable 18 to engagement with the limit switch 42 and is then clamped in position thereon by tightening its set screw 38. The boom is then lowered to its extreme downward position and the process is repeated for the other actuator 28, clamping it in the position on the cable where it just engages the limit switch 44. The boom is now ready for normal use and when it moves upward or downward to either extreme position the actuators will be moved linearly by the cable and the appropriate limit switch will be tripped. This will cause either valve 46 or 48 to be actuated and the clutch for the boom drive to disengage. For example, if the boom is inadvertently driven beyond its upper preset limit, the actuator 30 engages the limit switch 42 which causes the valve 46 to open. The hydraulic pressure in conduit 66 and at the slave actuator 68 immediately falls and the hydraulic fluid flows to the supply tank 78. The boom up clutch thus is disengaged and the boom movement is stopped. When the operator moves the control lever 50 in the boom down position, normal operation is restored. The boom down clutch is engaged. When the boom moves down the cable 18 moves the actuator away from the limit switch 42 and the valve 46 closes again.

To those skilled in the art to which this invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the spirit and scope of the invention. The disclosures and the description herein are purely illustrative and are not intended to be in any sense limiting.

I claim:

1. In combination with a load handling machine having a boom pivotally supported at one end thereon, drive means for raising and lowering the boom and clutch means operatively connected to said drive means, a device for automatically controlling the upward limit of travel of said boom about its pivotal axis comprising:

a flexible cable fixed atone end to said boom and movable by said boom;

a tension producing means connected to the other end of said cable and anchored to said machine;

a limit switch fixed to said machine adjacent said cable;

an adjustable actuator means attached to said cable including means for gripping the cable after being moved to a preselected location thereon and means for engaging and tripping said limit switch when said boom has moved to a predetermined angular position;

and means controlled by said limit switch for causing disengagement of the clutch from the drive means and thereby stopping the boom.

2. The device as described in claim 1 including a second limit switch fixed to said machine between the first limIt switch and the boom and a second adjustable actuator means on said cable for engaging and tripping said second limit switch when the boom is lowered to a predetermined limit position.

3. The device as described in claim 1 including means providing a longitudinal guide slot for maintaining said actuator in an upright position and properly aligned with said limit switch.

4. The device as described in claim 2 including a housing within said machine; a pair of pulleys fixed within said housing and spaced apart near its opposite ends, said cable engaging and partially wrapped around said pulleys; and means in said housing forming a guide slot for retaining said actuators in proper alignment.

5. The device as described in claim 1 wherein said tension producing means is a coil spring attached at one end to the end of said cable and anchored at its other end to said machine.

6. The device as described in claim 1 wherein said cable is secured to :a cylindrically shaped portion of said boom at its pivotal end, whereby upward or downward movement of said boom is proportional to a uniform linear rate of movement of said cable.

References Cited UNITED STATES PATENTS 2,126,118 8/1938 Kelley 212-39 2,393,312 1/1946 Davenport 21239 EVON C. BLUNK, Primary Examiner. H. C. HOR As stant Ex miner. 

1. IN COMBINATION WITH A LOAD HANDLING MACHINE HAVING A BOOM PIVOTALLY SUPORTED AT ONE END THEREON, DRIVE MEANS FOR RAISING AND LOWERING THE BOOM AND CLUTCH MEANS OPERATIVELY CONNECTED TO SAID DRIVE MEANS, A DEVICE FOR AUTOMATICALLY CONTROLLING THE UPWARD LIMIT OF TRAVEL OF SAID BOOM ABOUT ITS PIVOTAL AXIS COMPRISING: A FLEXIBLE CABLE FIXED AT ONE END TO SAID BOOM AND MOVABLE BY SAID BOOM; A TENSION PRODUCING MEANS CONNECTED TO THE OTHER END OF SAID CABLE AND ANCHORED TO SAID MACHINE; A LIMIT SWITCH FIXED TO SAID MACHINE ADJACENT SAID CABLE; AN ADJUSTABLE ACTUATOR MEANS ATTACHED TO SAID CABLE IN CLUDING MEANS FOR GRIPPING THE CABLE AFTER BEING MOVED TO A PRESELECTED LOCATION THEREON AND MEANS FOR ENGAGING AND TRIPPING SAID LIMIT SWITCH WHEN SAID BOOM HAS MOVED TO A PREDETERMINED ANGULAR POSITION; 